Lens unit of tv camera

ABSTRACT

A lens unit is attached to a body of a TV camera, and a main power supply of the camera body supplies power to motors that drive movable lenses of the lens unit. When the lens unit becomes unused, specifically, when the main power supply is turned off, or when the lens unit becomes detached from the camera body, a power supply switching part of the lens unit switches the power supply to an auxiliary power supply provided in the lens unit to allow the lens unit to operate. Then, a control circuit moves a focus lens and a zoom lens to an infinity end and a wide angle end, respectively, or to predetermined security positions, so as to prevent the deterioration of the operability and optical performance of the lens unit due to vibrations and shocks during transportation of the lens unit. Thereafter, the auxiliary power supply is turned off.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a lens unit of a TVcamera, and more particularly to a lens unit that automatically moves amovable lens to a security position when the lens unit becomes unused.

[0003] 2. Description of Related Art

[0004] A detachable lens unit of a TV camera is normally disconnectedfrom the camera after the camera is used if it is used outdoors, and thedetached lens unit is housed in a container during the transportation.If the TV camera is attached to a pedestal as is the case with a TVcamera that is used at a studio, the lens unit may be kept in theattached state during the transportation of the camera to a warehousefor example.

[0005] The lens unit is sometimes vibrated strongly and shocked while itis transported in the state of being housed in the container, or in thestate of being attached to the camera with the pedestal. In this case,gears and cam grooves, which drive movable lenses with a motor, maybecome loose, deteriorating the operability and optical performance ofthe lens unit. Moreover, the lens unit may be broken sometimes.

SUMMARY OF THE INVENTION

[0006] The present invention has been developed under theabove-described circumstances, and has as its object the provision of alens unit of a TV camera, which prevents the deterioration of theoperability and optical performance of the lens unit due to thevibrations and shocks during the transportation.

[0007] To achieve the above-mentioned object, the present invention isdirected to a lens unit of a TV camera, the lens unit being attached toa camera body of the TV camera, the lens unit comprising: at least onemovable lens, the movable lens being movable in a moving range duringshooting; a moving means for moving the movable lens; an ascertainingmeans for ascertaining whether the lens unit is used or unused; and acontrol means for driving the moving means to move the movable lens to apredetermined position when the ascertaining means detects that the lensunit becomes unused.

[0008] According to the present invention, when it is detected that thelens unit becomes unused, the movable lens is moved to the predeterminedposition. To ascertain whether the lens unit is used or unused, theascertaining means may ascertain whether a power supply of the camerabody is in operation or not, or the ascertaining means may ascertainwhether the lens unit is attached to the camera body or not.

[0009] The predetermined position may be within the moving range of themovable lens. The lens unit may permit looseness of positional accuracyof the movable lens at the predetermined position during shooting. Themoving means may be reinforced for the predetermined position of themovable lens. If the movable lens is a focus lens, the predeterminedposition may be an infinity end of the moving range of the focus lens.If the movable lens is a zoom lens, the predetermined position may be awide angle end of the moving range of the zoom lens.

[0010] The predetermined position may be outside the moving range of themovable lens. If the movable lens is the focus lens, the predeterminedposition may be beside the infinity end of the moving range of the focuslens. If the movable lens is the zoom lens, the predetermined positionmay be beside the wide angle end of the moving range of the zoom lens.

[0011] A stopper may be provided for limiting the movable range duringshooting. The limitation of the stopper is released to enable themovable lens to move to the predetermined position when the ascertainingmeans detects that the lens unit becomes unused.

[0012] The control means may drive the moving means to move the movablelens from the predetermined position to an initial position when theascertaining means detects that the lens unit becomes used. The initialposition may be a position of the movable lens when the ascertainingmeans detects that the lens unit becomes unused.

[0013] An auxiliary power supply may be provided for supplying power tothe lens unit when the ascertaining means detects that the lens unitbecomes unused. The auxiliary power supply may be turned off when themovable lens reaches the predetermined position, or when a predeterminedperiod of time has passed since the lens unit becomes unused. Theauxiliary power supply may be one of a condenser and a secondary batterythat are charged by the power supply of the camera body, or a primarybattery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The nature of this invention, as well as other objects andadvantages thereof, will be explained in the following with reference tothe accompanying drawings, in which like reference characters designatethe same or similar parts throughout the figures and wherein:

[0015]FIG. 1 is a view illustrating the structure of a TV cameraincluding a lens unit of the present invention;

[0016]FIG. 2 is a view showing the structure of a control system of alens unit according to the first embodiment of the present invention;

[0017]FIG. 3 is a flow chart showing a procedure for controlling thelens unit according to the first embodiment of the present invention;

[0018]FIG. 4 is a flow chart showing another procedure for controllingthe lens unit according to the first embodiment of the presentinvention;

[0019]FIG. 5 is a sectional view showing the structure of an opticalsystem of the lens unit according to the first embodiment of the presentinvention;

[0020]FIG. 6 is a front view showing the state wherein a zoom stopper isoperating;

[0021]FIG. 7 is a front view showing the state wherein the zoom stopperis not operating;

[0022]FIG. 8 is a view showing the structure of a control system of alens unit according to the second embodiment of the present invention;

[0023]FIG. 9 is a flow chart showing a procedure for controlling thelens unit according to the second embodiment of the present inventionwhen a power switch is turned off;

[0024]FIG. 10 is a flow chart showing a procedure for controlling thelens unit according to the second embodiment of the present inventionwhen the power switch is turned on;

[0025]FIG. 11 is a view showing the structure of a control system of alens unit according to the third embodiment of the present invention;

[0026]FIG. 12 is a flow chart showing a procedure for controlling thelens unit according to the third embodiment of the present inventionwhen the lens unit is detached from a camera body; and

[0027]FIG. 13 is a flow chart showing a procedure for controlling thelens unit according to the third embodiment of the present inventionwhen the lens unit is attached to the camera body.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] This invention will be described in further detail by way ofexample with reference to the accompanying drawings.

[0029]FIG. 1 shows the structure of a TV camera 10 including a lens unit12 according to the first embodiment of the present invention. As shownin FIG. 1, the TV camera 10 includes the lens unit 12 and a camera body14. The camera body 14 is provided with a view finder 16. The lens unit12 is detachable from the camera body 14, and the lens unit 12electrically connects to the camera body 14 through an interface.

[0030] The TV camera 10 is fixed on a tripod head 18, and a lenscontroller 26 for controlling zoom and focus is attached to a grip part24 of a pan/tilt rod 22 and a grip part of another pan/tilt rod (notshown). The lens controller 26 connects to the lens unit 12 through acable 28, and a user can adjust the zoom and focus by manipulating afocus demand and a zoom demand (a thumb ring 30) of the lens controller26 while looking at a captured image on the view finder 16.

[0031]FIG. 2 shows the structure of a control system of the lens unit12. The lens unit 12 includes optical members such as a focus lens 40, azoom lens 42, which is composed of a variable magnification lens 42A anda correction lens 42B, a diaphragm 44, an extender lens 46A for theequal focal length, an extender lens 46B for the twice focal length, anda master lens 48; driving circuits 50-56 and drive motors 60-66 fordriving the lenses and the diaphragm 44; detectors 70-76 and A/Dconverters 80-84 for determining the positions of the lenses and thediaphragm 44; and a control circuit 90 that controls each opticalmember. An imaging device 100 converts a subject image, which is formedon a light receiving surface through the optical members, into electricsignals. A signal processing circuit 102 performs a predetermined signalprocessing for the image signals input from the imaging device 100 andoutputs video signals to the view finder 16 and a video signal outputterminal 106. The imaging device 100 and the signal processing circuit102 are provided in the camera body 14.

[0032] As is well known, the variable magnification lens 42A of the zoomlens 42 changes the focal length of the lens unit 12, and the correctionlens 42B corrects the focal position of the lens unit 12 in such a waythat the focal position does not change. According to rotation of a zoomcam cylinder (not shown), the variable magnification lens 42A and thecorrection lens 42B are moved on the optical axis with a predeterminedrelation.

[0033] The control circuit 90 receives command signals from the lenscontroller 26 including such as the focus demand (a focus ring), thezoom demand (the thumb ring) and a diaphragm control. The controlcircuit 90 controls the movable lenses and the diaphragm 44 inaccordance with the command signals from the lens controller 26.

[0034] As shown in FIG. 2, the control circuit 90 connects to a mainpower supply 104 of the camera body 14 through an interface (not shown)and a power supply switching part 92 of the lens unit 12. When the mainpower supply 104 of the camera body 14 is in operation (normal mode),the main power supply 104 supplies the power to the control circuit 90,which supplies the power to the drive circuits 50-56 and the drivemotors 60-66 to actuate the drive motors 60-66. On the other hand, thelens unit 12 is provided with an auxiliary power supply 94 that connectsto the power supply switching part 92. The auxiliary power supply 94 maybe any type of power supply such as a primary battery, a secondarybattery and a condenser, as long as it can supply the power. If theauxiliary power supply 94 is a chargeable power supply such as thesecondary battery and the condenser, the main power supply 104 chargesthe auxiliary power supply 94 while the main power supply 104 is inoperation.

[0035] The power supply switching part 92 switches the power supplybetween the main power supply 104 and the auxiliary power supply 94.Specifically, when the main power supply 104 of the camera body 14 is inoperation, the main power supply 104 is connected to the control circuit90 so as to actuate the lens unit 12 including the driving circuits50-56 and the drive motors 60-66. On the other hand, when the main powersupply 104 of the camera body 14 is turned off after the camera 10 isused, the power supply is switched to the auxiliary power supply 94.

[0036] Thus, when the main power supply 104 is turned off, the controlcircuit 90 drives the lens unit 12 with the power from the auxiliarypower supply 94. Then, the drive motors 60 & 62 are actuated to move thefocus lens 40 and the zoom lens 42 to predetermined security positionsthat are an infinity end for focusing at infinity and a wide angle endfor providing the widest angle of shot, respectively, so as to avoidharmfulness of vibrations and shocks.

[0037] An explanation will be given of the security positions where thefocus lens 40 and the zoom lens 42 are positioned when the lens unit 12is not in use. When the lens unit 12 is housed or transported, themovable lenses such as the focus lens 40 and the zoom lens 42 arepreferably positioned at movement ends thereof, in other words, thepositions where the movable lenses are checked. In the vicinities of theinfinity end of the focus lens 40 and the wide angle end of the zoomlens 42 (actually, in the vicinities of the positions of the variablemagnification lens 42A and the correction lens 42B where the variablemagnification lens 42A and the correction lens 42B provide the widestangle of shot), the low positional accuracy of the focus lens 40 and thezoom lens 42 has a smaller effect on a captured image compared with aminimum object distance end and a telephoto end. If the positionalaccuracy of the focus lens 40 and the zoom lens 42 at the infinity endand the wide angle end were deteriorated by the strong vibrations andshocks while the lens unit 12 is transported, it would have a smalleffect on the operability and optical performance of the lens unit 12.

[0038] Hence, the infinity end and the wide angle end are determined asthe security positions where the focus lens 40 and the zoom lens 42 arepositioned when the lens unit 12 is not in use. When the main powersupply 104 is turned off on completion of the shooting, the focus lens40 and the zoom lens 42 are automatically moved to the infinity end andthe wide angle end, respectively, with the power of the auxiliarybattery 94. This prevents the operability and optical performance of thelens unit 12 from being deteriorated by the vibrations and shocks whilethe lens unit 12 is transported.

[0039] The focus lens 40 and the zoom lens 42 automatically move to theabove-mentioned security positions when the main power supply 104 isturned off. This saves the user from a lot of problems and improves thereliability compared to the case when the focus lens 40 and the zoomlens 42 are moved manually before the main power supply 104 is turnedoff after the shooting.

[0040] A description will be given of the control of the lens unit 12when the main power supply 104 of the camera body 14 is turned off. FIG.3 is a flow chart showing the procedure for controlling the lens unit 12when the main power supply 104 is turned off. The shooting is performedwhile the main power supply 104 is in operation. When the user turns offa switch of the main power supply 104 provided in the camera body 14,the main power supply 104 is turned off and the camera body 14 stopsworking (S10).

[0041] When the main power supply 104 is turned off, the power supplyswitching part 92 switches the power supply from the main power supply104 to the auxiliary power supply 94, which ensures the lens unit 12 tooperate (S12). The power supply switching part 92 may switch the powersupply automatically with use of a relay for example, or the controlcircuit 90 may control the power supply switching part 92 to switch thepower supply. To control the power supply switching part 92, the controlcircuit 90 must recognize that the main power supply 104 has been turnedoff. The recognition can be based on a signal from the camera body 14 asdescribed later.

[0042] When the power supply switching part 92 switches the power supplyfrom the main power supply 104 to the auxiliary power supply 94, thecontrol circuit 90 detects it in view of the state of the power supplyswitching part 92, the signal from the camera body 14, or the like. Forexample, the detection is based on reception of no response signal fromthe camera body 14, or on reception of a signal from the camera body 14indicating that the main power supply 94 is to be turned off.

[0043] The control circuit 90 outputs drive signals to the drivecircuits 50 & 52, and runs the drive motors 60 & 62 with the auxiliarypower supply 94 to thereby move the focus lens 40 and the zoom lens 42to the infinity end and the wide angle end, respectively (S14).

[0044] Then, the control circuit 90 determines the positions of thefocus lens 40 and the zoom lens 42 by means of the detectors 70 & 72 tothereby determine whether the focus lens 40 and the zoom lens 42 havereached the infinity end and the wide angle end, respectively (S16).When the control circuit 90 determines that the focus lens 40 and thezoom lens 42 have reached the infinity end and the wide angle end,respectively, the control circuit 90 stops the focus lens 40 and thezoom lens 42 and turns off the auxiliary power supply 94 (S18), and theprocessing is completed. To turn off the auxiliary power supply 94, thecontrol circuit 90 may control the power supply switching part 92 toswitch the power supply from the auxiliary power supply 94 to the mainpower supply 104, or the control circuit 90 may directly shut off thesupply of the power from the auxiliary power supply 94 to the powersupply switching part 92.

[0045] Thus, when the user turns off the main power supply 104 of thecamera body 14, the focus lens 40 and the zoom lens 42 moveautomatically to their security positions; the infinity end and the wideangle end. This causes the focus lens 40 and the zoom lens 42 to stop atthe security positions when the lens unit 12 is not in use. As statedabove, the operability and optical performance of the lens unit 12 canbe prevented from being deteriorated by the vibrations and shocks whilethe lens unit 12 is transported.

[0046] In the first embodiment, when the focus lens 40 and the zoom lens42 reach the infinity end and the wide angle end, respectively, theauxiliary power supply 94 is turned off according to the command fromthe control circuit 90, but the present invention is not restricted tothis. The auxiliary power supply 94 may be turned off automaticallywithout the command from the control circuit 90. For example, a timerlimits the time for supplying the power from the auxiliary power supply94, and the auxiliary power supply 94 is turned off when a preset timehas passed.

[0047] In the first embodiment, the auxiliary power supply 94 is used tomove the focus lens 40 and the zoom lens 42 to the infinity end and thewide angle end, respectively, when the main power supply 104 is turnedoff, but the present invention is not restricted to this. For example,when the user turns off the switch of the main power supply 104, thelens unit 12 does not allow the main power supply 104 to be turned offuntil the focus lens 40 and the zoom lens 42 reach the infinity end andthe wide angle end, respectively, then the focus lens 40 and the zoomlens 42 can be moved to the infinity end and the wide angle end oncompletion of the shooting without the use of the auxiliary power supply94 and the power supply switching part 92.

[0048]FIG. 4 is a flow chart illustrating the control procedure in theabove-mentioned case. When the user turns off the switch of the mainpower supply 104 (S50), the camera body 14 outputs a signal to the lensunit 12 to require the lens unit 12 to let the camera body 14 turn offthe main power supply 104 (S52). At this time, the camera body 14 doesnot turn off the main power supply 104 immediately, and the camera body14 keeps the main power supply 104 in operation until the lens unit 12permits the main power supply 104 to be turned off.

[0049] On reception of the signal, which requires the lens unit 12 tolet the main power supply 104 be turned off, the control circuit 90 ofthe lens unit 12 moves the focus lens 40 and the zoom lens 42 to theinfinity end and the wide angle end (S54).

[0050] Then, the control circuit 90 determines whether the focus lens 40and the zoom lens 42 have reached the infinity end and the wide angleend (S56). On detection that the focus lens 40 and the zoom lens 42 havereached the infinity end and the wide angle end, the control circuit 90outputs a signal that permits the camera body 14 to turn off the mainpower supply 104 (S58).

[0051] On reception of the signal, which permits the camera body 14 toturn off the main power supply 104, from the lens unit 12, the camerabody 14 turns off the main power supply 104 (S60) to stop the action ofthe camera 10.

[0052] As stated above, both the lens unit 12 and the camera body 14control the turning-off of the main power supply 104, and therefore, thefocus lens 40 and the zoom lens 42 can be moved to the securitypositions on completion of the shooting without the use of the auxiliarypower supply 94, etc.

[0053] In the first embodiment, the security positions of the focus lens40 and the zoom lens 42 are the infinity end and the wide angle end,respectively, but the present invention is not restricted to this. Thesecurity positions can be within the movable range of the focus lens 40and the zoom lens 42 during the shooting. For example, the securitypositions may be positions where the moving mechanisms (e.g. gears, cammembers) of the focus lens 40 and the zoom lens 42 are reinforced toresist against the vibrations and shocks. The security positions may beother positions where a relatively low positional accuracy of the focuslens 40 and the zoom lens 42 is required in view of the opticalcharacteristics of the lens unit 12.

[0054] In the first embodiment, the focus lens 40 and the zoom lens 42are positioned at the security positions when the lens unit 12 is not inuse, but the present invention is not restricted to this. At least oneof the focus lens, the zoom lens and another movable lens may bepositioned to a predetermined security position when the lens unit 12 isnot in use.

[0055] In the first embodiment, the lens unit 12 is detachable from thecamera body 14, but the lens unit may be integrated with the camerabody.

[0056] A description will be given of a lens unit according to thesecond embodiment of the present invention. The TV camera to which thelens unit according to the second embodiment is attached has the samestructure that was previously described with reference to FIG. 1, andthus, the entire structure of the camera will not be explained. FIG. 5is a sectional view illustrating the structure of an optical system inthe lens unit 112 according to the second embodiment. As shown in FIG.5, a focus lens 144, a zoom lens 146 composed of a variablemagnification lens 146A and a correction lens 146B, and a master lens148 are arranged in a lens barrel 140 from the front of the optical axis142 (from the left of the drawing).

[0057] A lens frame 150 holds the focus lens 144, and a guide pin 150Ais provided at the bottom end of the lens frame 150. The guide pin 150Ais guided on a guide groove 140A of the lens barrel 140 along theoptical axis 142. A focus drive screw 152 is rotatably attached to thetop end of the lens frame 150, and a gear 154 is secured to one end ofthe drive screw 152. The gear 154 is engaged with a gear 156 that issecured to a rotary shaft of a drive motor 160. Running the drive motor160 and rotating the focus drive screw 152 move the focus lens 144 alongthe optical axis 142.

[0058] Lens frames 170 & 172 hold the variable magnification lens 146Aand the correction lens 146B, respectively, of the zoom lens 146. Guidepins 170A & 172A are provided at the top ends of the lens frames 170 &172, and the guide pins 170A & 172A are guided on a guide groove 140B ofthe lens barrel 140 along the optical axis 142.

[0059] Cam followers 170B & 172B are provided at the bottom ends of thelens frames 170 & 172, and the cam followers 170B & 172B are fitted tocam grooves 174A & 174B of a zoom cam cylinder 174. A gear 176 issecured to one end of the zoom cam cylinder 174, and the gear 176 isengaged with a gear 178 that is secured to a rotary shaft of a drivemotor 162.

[0060] Running the drive motor 162 rotates the zoom cam cylinder 174,causing the cam followers 170B & 172B to follow the cam grooves 174A &174B and moving the variable magnification lens 146A and the correctionlens 146B with a predetermined relation.

[0061] A zoom stopper 180 is provided on the guide groove 140B, whichguides the guide pins 170A & 172A, and the zoom stopper 180 limits themovable range of the variable magnification lens 146A of the zoom lens146 at the wide angle side. The zoom stopper 180 is supported by thelens barrel 140 in such a way as to rotate about a shaft 180A, and agear 180B is formed on the peripheral surface of the zoom stopper 180 asshown in FIG. 6. The gear 180B is engaged with a gear 182 that issecured to a rotary shaft 164A of a drive motor 164. Running the drivemotor 164 swings the zoom stopper 180 about the shaft 180A.

[0062] When the lens unit 112 is in use (when the power supply is on),the zoom stopper 180 is fixed at such a position as to project partiallyinto the guide groove 140B, and limits the movable range of the guidepin 170A at the wide angle side as shown in FIGS. 5 and 6.

[0063] On the other hand, when the lens unit 112 is not in use (when thepower supply is off, which will be described later), the zoom stopper180 is turned with the drive motor 164 by 90° from the position shown inFIG. 6, and the zoom stopper 180 is fixed at such a position as not toproject into the guide groove 140B as shown in FIG. 7. Consequently, thevariable magnification lens 146A and the correction lens 146B of thezoom lens 146 are allowed to move to positions 184 beyond positionslimited by the zoom stopper 180 (a wide angle end) (the positions 184will hereinafter be referred to as security positions). Thus, the zoomlens 146 is positioned at the security position when the lens unit 112is not in use.

[0064] The cam grooves 174A & 174B of the zoom cam cylinder 174 extendto move the zoom lens 146 from the wide angle end limited by the zoomstopper 180 (in this case, the positions of the cam followers 170B &172B on the cam grooves 174A & 174B are shown with reference numerals186) to the security position (in this case, the positions of the camfollowers 170B & 172B on the cam grooves 174A & 174B are shown withreference numerals 188).

[0065] As is the case with the zoom lens 146, the movable range of thefocus lens 144 during the shooting is limited at the infinity side. Whenthe lens unit 112 is not in use (when the power supply is off), thefocus lens 144 is positioned at the security position (in this case, theposition of the guide pin 150A on the guide groove 140A is shown with areference numeral 190) beyond the limited position at the infinity side.

[0066]FIG. 8 shows the structure of a control system for the focus lens144 and the zoom lens 146 of the lens unit 112. As shown in FIG. 8, theoptical system of the lens unit 112 includes the optical members such asthe focus lens 144, the zoom lens 146 composed of the variablemagnification lens 146A and the correction lens 146B, the master lens148 and a diaphragm 149, and the zoom stopper 180. An imaging device 230converts a subject image, which is formed on a light receiving surfacethrough the optical members, into electric signals. A signal processingcircuit 232 performs a predetermined signal processing for the imagesignals input from the imaging device 230 and outputs video signals to aview finder and a video signal output terminal 206. The imaging device230 and the signal processing circuit 232 are provided in the camerabody 14.

[0067] A control system that controls the focus lens 144 and the zoomlens 146 includes drive circuits 200, 202 & 204 and the drive motors160, 162 & 164, which drive the focus lens 144, the zoom lens 146 andthe zoom stopper 180; detectors 206 & 208 and A/D converters 210 & 212,which determine the positions of the focus lens 144 and the zoom lens146; and a control circuit 220, which controls the above-mentionedmembers. A description will be omitted of the structures of the masterlens 148, the diaphragm 149, etc., which are also controlled by thecontrol circuit 220.

[0068] The control circuit 220 receives command signals from a lenscontroller 126 including such as the focus demand (the focus ring), thezoom demand (the thumb ring) and the diaphragm control. The controlcircuit 220 controls the movable lenses and the diaphragm 149 inaccordance with the command signals from the lens controller 126.

[0069] The control circuit 220 connects to a main power supply 234 ofthe camera body 14 through an interface (not illustrated) ad a powersupply switching part 222 of the lens unit 122. At the time of theshooting (when the main power supply 234 of the camera body 14 is inoperation), the main power supply 234 supplies the power to the controlcircuit 222, which supplies the power to the drive circuits 200 & 202,the drive motors 160 & 162, etc. to actuate the focus lens 144 and thezoom lens 146.

[0070] The lens unit 112 is provided with an auxiliary power supply 224that connects to the power supply switching part 222. The auxiliarypower supply 224 may be any type of power supply such as a primarybattery, a secondary battery and a condenser, as long as it can supplythe power. If the auxiliary power supply 224 is a chargeable powersupply such as the secondary battery and the condenser, the main powersupply 234 charges the auxiliary power supply 224 while the main powersupply 234 is in operation.

[0071] The power supply switching part 122 switches the power supplybetween the main power supply 234 and the auxiliary power supply 224.Specifically, when the main power supply 234 of the camera body 14 is inoperation, the main power supply 234 is connected to the control circuit220 so as to actuate the lens unit 112 and actuate the focus lens 144,the zoom lens 146, etc. On the other hand, when the main power supply234 of the camera body 14 is turned off after the camera 10 is used, thepower supply is switched to the auxiliary power supply 224.

[0072] Thus, when the main power supply 234 is turned off, the controlcircuit 220 drives the lens unit 112 with the power from the auxiliarypower supply 224. Then, the drive circuits 200 & 202 and the drivemotors 160 & 162 are actuated to move the focus lens 144 and the zoomlens 146 to the above-mentioned security positions. At this time, thedrive circuits 204 and the drive motors 164 are activated to release thelimitation of the zoom stopper 180 with respect to the movable range ofthe zoom lens 146.

[0073] An explanation will be given of the security positions for thefocus lens 144 and the zoom lens 146. As described previously, when thelens unit 112 is not in use (when the main power supply 234 of thecamera body 14 is not in operation), the focus lens 144 and the zoomlens 146 are positioned at the security positions (the position of thefocus lens 144 when the guide pin 150A is positioned at the position190, and the position of the zoom lens 146 when the guide pins 170A &172A are positioned at the positions 184 as shown in FIG. 5) at theinfinity side and the wide angle side, respectively, outside theirmovable range for the shooting (when the main power supply 234 of thecamera body 14 is in operation).

[0074] Hence, even if the focus drive screw 152 and the cam grooves 174A& 174B of the zoom cum cylinder 174 become loose due to the strongvibrations and shocks while the lens unit 112 is transported, it doesnot affect the movable range of the focus lens 144 and the zoom lens 146during the shooting. It is therefore possible to prevent thedeterioration of the operability and optical performances of the lensunit 112.

[0075] When the main power supply 234 is turned off, the focus lens 144and the zoom lens 146 move automatically to the security positions. Thissaves the user from a lot of problems, and the lens unit 112 can beprotected from the shocks during the transportation.

[0076] A description will be given of the control for the lens unit 112when the main power supply 234 of the camera body 14 is turned off. FIG.9 is a flow chart showing the procedure for controlling the lens unit112 when the main power supply 234 of the camera body 14 is turned off.The shooting is performed while the main power supply 234 is inoperation. When the user turns off a switch of the main power supply 234provided in the camera body 14, the main power supply 234 is turned offand the camera body 14 stops working (S70).

[0077] When the main power supply 234 is turned off, the power supplyswitching part 222 switches the power supply from the main power supply234 to the auxiliary power supply 224, which ensures the lens unit 112to operate (S72). The power supply switching part 222 may switch thepower supply automatically with use of a relay for example, or thecontrol circuit 220 may control the power supply switching part 222 toswitch the power supply. To control the power supply switching part 222,the control circuit 220 must recognize that the main power supply 234has been turned off. The recognition can be based on the state of thepower supply switching part 222 and a signal from the camera body 14 asdescribed later.

[0078] When the power supply switching part 222 switches the powersupply from the main power supply 234 to the auxiliary power supply 224,the control circuit 220 detects it in view of the state of the powersupply switching part 222, the signal from the camera body 14, or thelike. For example, the detection is based on reception of no responsesignal from the camera body 14, or on reception of a signal from thecamera body 14 indicating that the main power supply 234 is to be turnedoff.

[0079] Then, the control circuit 220 outputs a drive signal to the drivecircuit 204, and runs the drive motor 164 with the auxiliary powersupply 224 to release the zoom stopper 180 (S74). This allows the zoomlens 146 to move to the security position.

[0080] Thereafter, the control circuit 220 outputs drive signals to thedrive circuits 200 & 202, and runs the drive motors 160 & 162 with theauxiliary power supply 224 to thereby move the focus lens 144 and thezoom lens 146 to the security positions at the infinity side and thewide angle side, respectively (S76).

[0081] Then, the control circuit 220 determines the positions of thefocus lens 144 and the zoom lens 146 by means of the detectors 206 & 208to thereby determine whether the focus lens 144 and the zoom lens 146have reached the security positions (S78). If the focus lens 144 and thezoom lens 146 have reached the security positions, the control circuit220 stops them (S80) and turns off the auxiliary power supply 224 (S82),and the processing is completed. To turn off the auxiliary power supply224, the control circuit 220 may control the power supply switching part222 to switch the power supply from the auxiliary power supply 224 tothe main power supply 234, or the control circuit 220 may directly shutoff the supply of the power from the auxiliary power supply 224 to thepower supply switching part 222.

[0082] Thus, when the user turns off the main power supply 234 of thecamera body 14, the focus lens 144 and the zoom lens 146 moveautomatically to the security positions.

[0083] A description will be given of the control procedure when themain power supply 234 is turned on in the state wherein the focus lens144 and the zoom lens 146 are positioned at the security positions withreference to a flow chart of FIG. 10. When the user turns on the switchof the main power supply 234 provided in the camera body 14, the mainpower supply 234 is turned on and the camera 10 starts operation (S90).

[0084] When the main power supply 234 is turned on, the power supplyswitching part 222 connects the main power supply 234 to the controlcircuit 220. This activates the control circuit 220 (S92), and thecontrol circuit 220 executes the initialization of the lens unit 112 asdescribed below.

[0085] At the start of the initialization, the control circuit 220outputs drive signals to the drive circuits 200 & 202, and runs thedrive motors 160 & 162 to move the focus lens 144 and the zoom lens 146from the security positions to preset initial positions (S94). Forexample, the preset positions of the focus lens 144 and the zoom lens146 may be the infinity end and the wide angle end, respectively, in theshooting. The user may set the preset positions with an adjuster. It isalso possible to memorize, in a memory, the positions of the focus lens144 and the zoom lens 146 as the preset positions when the main powersupply 234 is turned off so that the focus lens 144 and the zoom lens146 can return the memorized positions when the main power supply 234 isturned on.

[0086] The control circuit 220 determines whether the focus lens 144 andthe zoom lens 146 have reached the preset positions with the detectors206 & 208 (S96). If the focus lens 144 and the zoom lens 146 havereached the preset positions, the control circuit 220 stops them (S98).Thereafter, the master lens 148 may be driven by a drive mechanism (notshown) to initialize a focus.

[0087] Then, the control circuit 220 outputs a drive signal to the drivecircuit 204, and runs the drive motor 164 to activate the zoom stopper180 so as to limit the movable range of the zoom lens 146 at the wideangle side (S100).

[0088] Thus, the control circuit 220 completes the initialization of thelens unit 112, and switches to a mode for the normal shooting (a normalmode) (S102). If the control circuit 220 moves the focus lens 144 andthe zoom lens 146 to the preset positions by positional control in theinitialization, the control is switched to the normal control by thelens controller 126 in the normal mode, in other words, the focus lens144 is positional-controlled and the zoom lens 146 is rate-controlled.

[0089] As a result of the above processing, the focus lens 144 and thezoom lens 146 return from the security positions to the movable range inthe shooting, thus enabling the shooting.

[0090] As stated above, in the second embodiment, when the focus lens144 and the zoom lens 146 reach the security positions after the mainpower supply 234 is turned off, the auxiliary power supply 234 is turnedoff according to the command from the control circuit 220, but thepresent invention is not restricted to this. The auxiliary power supply224 may be turned off automatically without the command from the controlcircuit 220. For example, a timer limits the time for supplying thepower from the auxiliary power supply 224, and the auxiliary powersupply 224 is turned off when a preset time has passed.

[0091] In the second embodiment, the auxiliary power supply 224 is usedto move the focus lens 144 and the zoom lens 146 to the securitypositions when the main power supply 234 is turned off, but the presentinvention is not restricted to this. For example, when the user turnsoff the switch of the main power supply 234, the lens unit 112 does notallow the main power supply 234 to be turned off until the focus lens144 and the zoom lens 146 reach the security positions, then the focuslens 144 and the zoom lens 146 can be moved to the security positions oncompletion of the shooting without the use of the auxiliary power supply224 and the power supply switching part 222.

[0092] In the second embodiment, the security positions of the focuslens 144 and the zoom lens 146 are provided beyond the infinity end andthe wide angle end, respectively, but the present invention is notrestricted to this. The security positions of the focus lens 144 and thezoom lens 146 may be provided beyond the minimum object distance end andthe telephoto end, respectively.

[0093] In the second embodiment, the focus lens 144 and the zoom lens146 are positioned at the security positions when the lens unit 112 isnot in use, but the present invention is not restricted to this. Whenthe lens unit 112 is not in use, at least one of the focus lens, thezoom lens and another movable lens (e.g. the master lens 148) may bepositioned to a predetermined security position that is unused duringthe shooting.

[0094] In the second embodiment, only the zoom lens 146 is provided withthe zoom stopper 180, which limits the movable range of the zoom lens146 during the shooting, but the focus lens 144 may also be providedwith a stopper that limits the movable range of the focus lens 144during the shooting.

[0095] In the second embodiment, the lens unit 112 is detachable fromthe camera body 14, but the lens unit 112 may be integrated with thelens unit 12.

[0096] A description will be given of a lens unit according to the thirdembodiment of the present invention. The third embodiment has the samestructures of the TV lens, the optical system and the zoom stopper thatwere described previously with reference to FIGS. 1, 5, 6 and 7, andthus, they will not be described. Parts similar to those described withreference to FIGS. 1, 5, 6 and 7 are denoted by the same referencenumerals. In the second embodiment shown in FIGS. 5, 6 and 7, when themain power supply of the camera is turned off, the zoom stopper is movedto the position indicated in FIG. 7 and the movable lenses are moved tothe security positions. In the third embodiment, the zoom stopper ismoved to the position indicated in FIG. 7 and the movable lenses aremoved to the security positions when the lens unit 112 becomes detachedfrom the camera body 14.

[0097]FIG. 11 shows the structure of a control system for the focus lens144 and the zoom lens 146 of the lens unit 112 according to the thirdembodiment. FIG. 11 is substantially the same as FIG. 8, and adescription will be given of the structure and operation that aredifferent from those described with reference to FIG. 8. A connectiondetecting part 226 connects to the power supply switching part 222,which connects to the main power supply 234 of the camera body 14 andthe auxiliary power supply 224 of the lens unit 112. For example, theconnection detecting part 226 has a switch provided at a position wherethe lens unit 112 connects to the camera body 14. If the lens unit 112is attached to the camera body 14, the switch is OFF, and if the lensunit 112 is not attached to the camera body 14, the switch is ON.

[0098] The power supply switching part 222 switches the power supplythat is connected to the control circuit 220 between the main powersupply 234 and the auxiliary power supply 224 in accordance with thestate of the switch of the connection detecting part 226. When theswitch of the connection detecting part 226 is OFF, in other words, whenthe lens unit 112 is attached to the camera body 14, the main powersupply 234 is connected to the control circuit 220 to activate the focuslens 144, the zoom lens 146, etc. Then, when the switch of theconnection detecting part 226 is turned on, in other words, when thelens unit 112 becomes detached from the camera body 14, the power supplyswitching part 222 connects the auxiliary power supply 224 to thecontrol circuit 220.

[0099] Thus, when the lens unit 112 becomes detached from the camerabody 14, the control circuit 220 drives the lens unit 112 with the powerfrom the auxiliary power supply 224, and activates the drive circuits200 & 202 and the drive motors 160 & 162, which move the focus lens 144and the zoom lens 146 to the security positions. At this time, the drivecircuit 204 and the drive motor 164 are activated to release thelimitation of the zoom stopper 180 with respect to the movable range ofthe zoom lens 146.

[0100] When the lens unit 112 is detached from the camera body 14, thefocus lens 144 and the zoom lens 146 are positioned at the securitypositions beyond the infinity end and the wide angle end of the movablerange in the shooting (the position of the focus lens 144 when the guidepin 150A is positioned at the position 190, and the position of the zoomlens 146 when the guide pins 170A & 172A are positioned at the positions184 as shown in FIG. 5). Hence, even if the focus drive screw 152 andthe cum grooves 174A & 174B of the zoom cam cylinder 174 become loosedue to the strong vibrations and shocks while the lens unit 112 istransported independently of the camera body 14, it does not affect themovable range of the focus lens 144 and the zoom lens 146 in theshooting. It is therefore possible to prevent the deterioration of theoperability and optical performances of the lens unit 112.

[0101] When the lens unit 112 becomes detached from the camera body 14,the focus lens 144 and the zoom lens 146 move automatically to thesecurity positions. This saves the user from a lot of problems, and thelens unit 12 can be protected from the shocks during the transportation.

[0102] A description will be given of the control for the lens unit 12when it becomes detached from the camera body 14. FIG. 12 is a flowchart showing the procedure for controlling the lens unit 112 when it isdetached from the camera body 14. When the lens unit 112 becomesdetached from the camera body 14 on completion of the shooting (S110),the switch of the connection detecting part 226 is turned on, causingthe power supply switching part 222 to switch the power supply from themain power supply 234 to the auxiliary power supply 224, which ensuresthe lens unit 112 to operate (S112).

[0103] When the power supply switching part 222 switches the powersupply to the auxiliary power supply 224, the control circuit 220detects it in view of the state of the power supply switching part 222or the connection detecting part 226, the signal from the camera body14, or the like. For example, the detection is based on reception of noresponse signal from the camera body 14, or on reception of a signalfrom the camera body 14 indicating that the main power supply 234 is tobe turned off.

[0104] Then, the control circuit 220 outputs a drive signal to the drivecircuit 204, and runs the drive motor 164 with the auxiliary powersupply 224 to release the zoom stopper 180 (S114). This allows the zoomlens 146 to move to the security position.

[0105] Thereafter, the control circuit 220 outputs drive signals to thedrive circuits 200 & 202, and runs the drive motors 160 & 162 with theauxiliary power supply 224 to thereby move the focus lens 144 and thezoom lens 146 to the security positions at the infinity side and thewide angle side, respectively (S116).

[0106] Then, the control circuit 220 determines the positions of thefocus lens 144 and the zoom lens 146 by means of the detectors 206 & 208to thereby determine whether the focus lens 144 and the zoom lens 146have reached the security positions (S118). If the focus lens 144 andthe zoom lens 146 have reached the security positions, the controlcircuit 220 stops them (S120) and turns off the auxiliary power supply224 (S122), and the processing is completed. To turn off the auxiliarypower supply 224, the control circuit 220 may control the power supplyswitching part 222 to switch the power supply from the auxiliary powersupply 224 to the main power supply 234, or the control circuit 220 maydirectly shut off the supply of the power from the auxiliary powersupply 224 to the power supply switching part 222.

[0107] Thus, when the lens unit 112 becomes detached from the camerabody 14, the focus lens 144 and the zoom lens 146 move automatically tothe security positions.

[0108] A description will be given of the control for the lens unit 112when the main power supply 234 of the camera body 14 is turned on afterthe lens unit 112 is attached to the camera body 14. FIG. 13 is a flowchart showing the procedure for controlling the lens unit 112 when themain power supply 234 of the camera body 14 is turned on after the lensunit 112 is attached to the camera body 14. When the lens unit 112 isattached to the camera body 14 (S128), the switch of the connectiondetecting part 226 is turned off, causing the power supply switchingpart 222 to connect the main power supply 234 to the control circuit220.

[0109] When the user turns on the switch of the main power supply 234provided in the camera body 14, the main power supply 234 is turned onto cause the camera 10 to start working (S130) and cause the controlcircuit 220 to start working (S132). Then, the control circuit 220executes the initialization of the lens unit 112 as described below.

[0110] At the start of the initialization, the control circuit 220outputs drive signals to the drive circuits 200 & 202, and runs thedrive motors 160 & 162 to move the focus lens 144 and the zoom lens 146from the security positions to preset initial positions (S134). Forexample, the preset positions of the focus lens 144 and the zoom lens146 may be the infinity end and the wide angle end, respectively, in theshooting. The user may set the preset positions with an adjuster. It isalso possible to memorize, in a memory, the positions of the focus lens144 and the zoom lens 146 as the preset positions when the main powersupply 234 is turned off so that the focus lens 144 and the zoom lens146 can return the memorized positions when the main power supply 234 isturned on.

[0111] The control circuit 220 determines whether the focus lens 144 andthe zoom lens 146 have reached the preset positions with the detectors206 & 208 (S136). If the focus lens 144 and the zoom lens 146 havereached the preset positions, the control circuit 220 stops them (S138).Thereafter, the master lens 148 may be driven by a drive mechanism (notshown) to initialize a focus.

[0112] Then, the control circuit 220 outputs a drive signal to the drivecircuit 204, and runs the drive motor 164 to activate the zoom stopper180 so as to limit the movable range of the zoom lens 146 at the wideangle side (S140).

[0113] Thus, the control circuit 220 completes the initialization of thelens unit 112, and switches to a mode for the normal shooting (a normalmode) (S142). If the control circuit 220 moves the focus lens 144 andthe zoom lens 146 to the preset positions by positional control in theinitialization, the control is switched to the normal control by thelens controller 126 in the normal mode, in other words, the focus lens144 is positional-controlled and the zoom lens 146 is rate-controlled.

[0114] As a result of the above processing, the focus lens 144 and thezoom lens 146 return from the security positions to the movable range inthe shooting, thus enabling the shooting.

[0115] In the flow chart of FIG. 13, the focus lens 144 and the zoomlens 146 do not return to the movable range in the shooting until themain power supply 234 of the camera body 14 is turned on after the lensunit 112 is attached to the camera body 14; however, the presentinvention is not restricted to this. When the lens unit 112 becomesattached to the camera body 14, the focus lens 144 and the zoom lens 146may return to the preset positions with the power of the auxiliary powersupply 224 whether the main power supply 234 of the camera body 14 is inoperation or not.

[0116] In the third embodiment, when the focus lens 144 and the zoomlens 146 reach the security positions after the lens unit 112 becomesdetached from the camera body 14, the auxiliary power supply 234 isturned off according to the command from the control circuit 220, butthe present invention is not restricted to this. The auxiliary powersupply 224 may be turned off automatically without the command from thecontrol circuit 220. For example, a timer limits the time for supplyingthe power from the auxiliary power supply 224, and the auxiliary powersupply 224 is turned off when a preset time has passed.

[0117] In the third embodiment, the security positions of the focus lens144 and the zoom lens 146 are provided beyond the infinity end and thewide angle end, respectively, but the present invention is notrestricted to this. The security positions of the focus lens 144 and thezoom lens 146 may be provided beyond the minimum object distance end andthe telephoto end, respectively.

[0118] In the third embodiment, the focus lens 144 and the zoom lens 146are positioned at the security positions when the lens unit 112 is notin use, but the present invention is not restricted to this. When thelens unit 112 is not in use, at least one of the focus lens, the zoomlens and another movable lens (e.g. the master lens 148) may bepositioned to a predetermined security position that is unused duringthe shooting.

[0119] In the third embodiment, only the zoom lens 146 is provided withthe zoom stopper 180, which limits the movable range of the zoom lens146 during the shooting, but the focus lens 144 may also be providedwith a stopper that limits the movable range of the focus lens 144during the shooting.

[0120] In the third embodiment, the security positions of the focus lens144 and the zoom lens 146 are outside the movable range of the lenses inthe shooting, but the present invention is not restricted to this. As isthe case with the first embodiment, the security positions can be in themovable range of the focus lens 144 and the zoom lens 146 in theshooting. For example, the security positions may be positions where themoving mechanisms (e.g. gears, cam members) of the focus lens 144 andthe zoom lens 146 are reinforced to resist against the vibrations andshocks. The security positions of the focus lens 144 and the zoom lens146 may be the infinity end and the wide angle end, respectively.Specifically, in the vicinities of the infinity end of the focus lens144 and the wide angle end of the zoom lens 146, the low positionalaccuracy of the focus lens 144 and the zoom 146 has a smaller effect ona captured image compared with the minimum object distance end and thetelephoto end. If the positional accuracy of the focus lens 144 and thezoom lens 146 at the infinity end and the wide angle end weredeteriorated by the strong vibrations and shocks while the lens unit 112is transported, it would have a small effect on the operability andoptical performance of the lens unit 112.

[0121] Consequently, providing the security positions of the focus lens144 and the zoom lens 146 at the infinity end and the wide angle endprevents the deterioration of the operability and optical performance ofthe lens unit 112 due to the vibrations and shocks.

[0122] Even if the movable lenses are positioned in their movable rangein the shooting when the lens unit is not in use, the focus lens 144 andthe zoom lens 146 may be moved to the preset positions (e.g. thepositions of the focus lens 144 and the zoom lens 146 when the lens unit112 becomes detached form the camera body 14) when the lens unit 112becomes attached to the camera body 14, or when the main power supply234 of the camera body 14 is turned on after the lens unit 112 isattached to the camera body 14.

[0123] As set forth hereinabove, if the lens unit of the TV cameraaccording to the present invention detects that the power supply of thecamera body is to be turned off when the user turns off the switch ofthe power supply, the motor is run to move at least one of the focuslens and the zoom lens to the security position where the vibrations andshocks do not affect the operability and optical performance of the lensunit. Thus, whenever the lens unit is unused, the focus lens and/or thezoom lens are positioned at the security positions, and it is thereforepossible to prevent the deterioration of the operability and opticalperformance of the lens unit due to the vibrations and shocks during thetransportation, etc.

[0124] For example, the security positions of the focus lens and thezoom lens are the infinity end and the wide angle end, respectively.Since these positions permit a relatively large error in the positionaladjustment of the lenses, the low positional accuracy of the lenses atthese positions would give only a smaller effect on the operability andoptical performance of the lens unit.

[0125] Since the lens unit is provided with the auxiliary power supply,the motors can be run with the power of the auxiliary power supply tomove the focus lens and the zoom lens to the security positions afterthe power supply of the camera body has been turned off.

[0126] According to another mode, when the power supply of the TV camerais turned off, at least one of the focus lens and the zoom lens movesautomatically to the security position outside its movable range in theshooting. Thus, whenever the power supply of the TV camera is not inoperation, the focus lens and/or the zoom lens can be positioned at thesecurity positions. The looseness at the security positions would notaffect the operability and optical performance of the lens unit sincethe security positions are not used as the movable range of the lensesduring the shooting. It is therefore possible to protect the lens unitfrom the shocks, etc. during the transportation.

[0127] According to yet another mode, when the lens unit becomesdetached from the TV camera, at least one of the focus lens and the zoomlens moves automatically to the security position. Thus, whenever thelens unit is transported independently of the TV camera, the focus lensand/or the zoom lens are positioned at the security positions. Thissaves the user from a lot of problems, and prevents the deterioration ofthe operability and optical performance of the lens unit due to theshocks, etc. during the transportation.

[0128] It should be understood, however, that there is no intention tolimit the invention to the specific forms disclosed, but on thecontrary, the invention is to cover all modifications, alternateconstructions and equivalents falling within the spirit and scope of theinvention as expressed in the appended claims.

What is clamed is:
 1. A lens unit for a TV camera, the lens unit beingattached to a camera body of the TV camera, the lens unit comprising: atleast one movable lens, the movable lens being movable in a moving rangeduring shooting; moving means for moving the movable lens; ascertainingmeans for ascertaining whether the lens unit is used or unused; andcontrol means for driving the moving means to move the movable lens to apredetermined position when the ascertaining means detects that the lensunit becomes unused.
 2. The lens unit of claim 1, wherein theascertaining means ascertains whether a power supply of the camera bodyis in operation or not to ascertain whether the lens unit is used orunused.
 3. The lens unit of claim 1, wherein the ascertaining meansascertains whether the lens unit is attached to the camera body or notto ascertain whether the lens unit is used or unused.
 4. The lens unitof claim 1, wherein the predetermined position is within the movingrange.
 5. The lens unit of claim 4, wherein the lens unit permitslooseness of positional accuracy of the movable lens at thepredetermined position during shooting.
 6. The lens unit of claim 4,wherein the moving means is reinforced for the predetermined position ofthe movable lens.
 7. The lens unit of claim 4, wherein the movable lensis a focus lens, and the predetermined position is an infinity end ofthe moving range of the focus lens.
 8. The lens unit of claim 4, whereinthe movable lens is a zoom lens, and the predetermined position is awide angle end of the moving range of the zoom lens.
 9. The lens unit ofclaim 1, wherein the predetermined position is outside the moving range.10. The lens unit of claim 9, wherein the movable lens is a focus lens,and the predetermined position is beside an infinity end of the movingrange of the focus lens.
 11. The lens unit of claim 9, wherein themovable lens is a zoom lens, and the predetermined position is beside awide angle end of the moving range of the zoom lens.
 12. The lens unitof claim 9, further comprising a stopper for limiting the movable rangeduring shooting, wherein the limitation of the stopper is released toenable the movable lens to move to the predetermined position when theascertaining means detects that the lens unit becomes unused.
 13. Thelens unit of claim 1, wherein the control means drives the moving meansto move the movable lens from the predetermined position to an initialposition when the ascertaining means detects that the lens unit becomesused.
 14. The lens unit of claim 13, wherein the initial position is aposition of the movable lens when the ascertaining means detects thatthe lens unit becomes unused.
 15. The lens unit of claim 1, furthercomprising an auxiliary power supply for supplying power to the lensunit when the ascertaining means detects that the lens unit becomesunused.
 16. The lens unit of claim 15, wherein the auxiliary powersupply is turned off when the movable lens reaches the predeterminedposition.
 17. The lens unit of claim 15, wherein the auxiliary powersupply is turned off when a predetermined period of time has passedsince the lens unit becomes unused.
 18. The lens unit of claim 15,wherein the auxiliary power supply is one of a condenser and a secondarybattery charged by a power supply of the camera body.
 19. The lens unitof claim 15, wherein the auxiliary power supply is a primary battery.